Deterministic Lateral Displacement Devices Research Articles

Trajectory analysis of circulating tumor cells through contorted deterministic lateral displacement array for unruptured trapping: a simulation study

During the multistage process of cancer spread, fragments of cells branch out from the primitive tumor tissue and scatter throughout the body by blood flow stream or lymph, which are termed as circulating tumor cells (CTCs), regarded as an important biomarker for early cancer diagnosis. Deterministic lateral displacement (DLD) is one of the most efficient passive type particle isolation techniques which functions on asymmetrical laminar flow diversion around the placed microposts forming an array, based on the critical dimeter of the device. In this simulation study, complete trajectory analysis of CTCs and WBCs has been performed using COMSOL Multiphysics software with respect to the angular orientation of sample inlet channel. A simulated model of an asymmetric DLD array-based microfluidic device with latest empirical expression for critical diameter has been presented with optimized sample inlet orientation so as to maintain perfect separation efficiency of CTCs along with arrangement for unruptured trapping of CTCs and WBCs. The approximate CTC isolation efficiency was obtained above 95% for sample inlet inclinations up to 0.5°, and further tilt showed reduction in efficiency. Migration angle of CTC trajectory for the modeled device was obtained around 15° for both the sample inlet orientations leading to least intermingling of CTCs and WBCs. A smaller number of CTC–WBC interaction points was observed for clockwise sample inlet tilt compared to the anticlockwise displacement reducing possibilities of cell rupture. The shear rate around central microposts was found to be higher as well in clockwise sample inlet orientation. This simulation study establishes that sample inlet clockwise tilting of maximum around 0.5°–0.7° leads to better CTC isolation and provides better chances of unruptured trapping of cells at the designated outlets. The results of this study provide an approach toward further optimization of DLD devices' functioning and, thus, could help fabricate better DLD-based microfluidic devices for efficient trapping of CTCs.

Investigating the impact of pillar shape on flexible erythrocyte separation through deterministic lateral displacement

The deterministic lateral displacement (DLD) method has gradually moved beyond the separation of spherical rigid particles and has been successfully applied to the field of biological cells, especially to the separation of disc-shaped flexible erythrocytes. Different shapes of micropillars in the DLD device significantly affect the sorting performance of erythrocytes. We investigated the effect of the flow field in the gap of micropillars of different shapes (circular, triangular, I-shaped) on the behavior of erythrocyte tumbling motion. The simulation results showed that in the I-shaped pillar DLD device, compared with the circular and triangular pillars, the erythrocytes exhibited a stable and continuous flipping motion during the movement along the array offset direction, which enabled the effective separation size to be maintained at a high level. In addition, the formula for calculating the critical diameter of the I-shaped pillar DLD array for separating erythrocytes was obtained by fitting, which provides strong support for a more efficient design of the I-shaped pillar DLD device dedicated to erythrocyte sorting.

On-chip label-free sorting and enrichment of microplastic particles by using deterministic lateral displacement

A novel deterministic lateral displacement (DLD) method employing a pressure-driven flow for the continuous size-based separation of microplastic particles is presented in this paper. To induce the DLD effect, arrays of triangular posts were designed to enhance the sorting resolution and reduce the particles clogging. For the particles with a diameter larger than the critical diameter (Dc) in the DLD device, they move in bump mode with collision to microposts. While, the particles flow in zigzag mode if their sizes are below the Dc value. The DLD microfluidic chip enables simplified fabrication process and shows property of label-free and high throughput. Numerical studies were conducted to discuss the Dc values in the microchannel with horizontally symmetrical and asymmetrical posts, where Dc was found smaller in the asymmetric horizontal flow, enabling higher separation sensitivity and resolution. Experiments were conducted to demonstrate the separation of 10 μm and 15 μm polystyrene microplastic particles, and different types of polystyrene and polyethylene microplastic particles by adjusting the flow rates. In order to achieve successful separation, the flow rates between the sheath flow and the sample solution were well matched. In this way, the proposed DLD microfluidic chip with horizontally asymmetrical triangular posts shows property of label-free, high throughput, capability to analyze microplastic particle selectively and sensitively, possibility of sorting nanoplastic particles.

Rapid cell isolation in breastmilk in a non-clinical setting by a deterministic lateral displacement device and selective water and fat absorption.

Breastmilk is a reliable source of biomarker-containing, sloughed breast cells that have the potential to give valuable health insights to new mothers. Furthermore, known DNA-based markers for pregnancy-associated breast cancer are chemically stable and can be safely stored on a commercially available FTA® Elute Micro (EM) card, which can subsequently be mailed to a testing facility for the cost of a stamp. In theory, this archiving process can be performed by nonprofessionals in very low-resource settings as it simply requires placing a drop of breastmilk on an EM card. Although this level of convenience is paramount for new mothers, the low cell density of breastmilk complicates archiving on an EM card as such commercial products and associated protocols were designed for high-cell density physiological fluids such as blood. In this study, we present the use of a deterministic lateral displacement (DLD) device combined with porous superabsorbent polymers and hydrophobic sponges to achieve simple and low-cost cell enrichment in breastmilk. As the critical separation diameter in a DLD device is more heavily dependent on lithographically controlled pillar layout than fluid or flow properties, our use of DLD microfluidics allowed for the accommodation of both varying viscosities in human breastmilk samples and a varying pressure of actuation resulting from manual, syringe-driven operation. We demonstrate successful cell enrichment (>11×) and a corresponding increase in the DNA concentration of EM card elutions among breastmilk samples processed with our hybrid microfluidic system. As our device achieves sufficiently high cell enrichment in breastmilk samples while only requiring the user to push a syringe for 4 min with reasonable effort, we believe that it has high potential to expand EM card DNA archiving for diagnostic applications with low-cell density physiological fluids and in low-resource settings.

Isolation of Extracellular Vesicles from Cell Culture and Blood Through Nano-Targeted DLD Microfluidic Device.

Extracellular vesicles (EVs) are secreted by cells and found in biological fluids such as blood, with concentration correlated with oncogenic signals, making them attractive biomarkers for liquid biopsy. The current gold-standard method for EVs isolation requires an ultracentrifugation (UC) step among others. The cost and complexity of this technique are forbiddingly high for many researchers, as well as for routine use in biological laboratories and hospitals. This chapter reports on a simple microfluidic method for EVs isolation, based on a microfluidic size sorting technique named Deterministic Lateral Displacement (DLD). With the design of micrometric DLD array, we demonstrated the potential of our DLD devices for the isolation of nano-biological objects such as EVs, with main population size distribution consistent with UC technique.

Unraveling the motion and deformation characteristics of red blood cells in a deterministic lateral displacement device

Deterministic Lateral Displacement (DLD) device has gained widespread recognition and trusted for filtering blood cells. However, there remains a crucial need to explore the complex interplay between deformable cells and flow within the DLD device to improve its design. This paper presents an approach utilizing a mesoscopic cell-level numerical model based on dissipative particle dynamics to effectively capture this complex phenomenon. To establish the model’s credibility, a series of numerical simulations were conducted and the numerical results were validated with nominal experimental data from the literature. These include single cell stretching experiment, comparisons of the morphological characteristics of cells in DLD, and comparison the specific row-shift fraction of DLD required to initiate the zigzag mode. Additionally, we investigate the effect of cell rigidity, which serves as an indicator of cell health, on average flow velocity, trajectory, and asphericity. Moreover, we extend the existing theory of predicting zigzag mode for solid spherical particles to encompass the behavior of red blood cells. To achieve this, we introduce a new concept of effective diameter and demonstrate its applicability in providing highly accurate predictions across a wide range of conditions.

Mesoscopic simulation of multi-scheme particle separation in deterministic lateral displacement devices using two-piece hybrid pillars

Pillar shape exploration in deterministic lateral displacement (DLD) technique holds great promise for developing high-performance microfluidic devices with versatile sorting schemes. A recent innovative design using filter-like micropillars was proposed to improve cell separation, but its significance might be greatly underestimated due to an inaccurate understanding of the underlying mechanism. In this study, we employ mesoscopic hydrodynamic simulations to explore the movement and separation of rigid spherical particles in DLD arrays using various two-piece hybrid (TPH) pillars, where each pillar consists of two individual pieces separated by a tunable inter-piece channel. In comparison with the conventional one-piece pillars, the back piece of TPH-pillars is found to hierarchically tailor the flow profile of the front piece on the basis of the row shift fraction and the inter-piece channel width, resulting in unique tunable multi-scheme separation at low, intermediate, and high row shift fractions, respectively. At the intermediate regime, in particular, the first flow lane that determines the critical separation size could be physically fenced out by the inter-piece channel, and a delicate coupling of hydrodynamic filtration and DLD has been revealed to induce a constant critical size in the whole regime. This work theoretically demonstrates the feasibility and significance of TPH-pillars, which may open up a new direction of the geometry design by exploiting rich multi-piece hybrid structures to expand the versatility of the DLD technique.

Stiffness influence on particle separation in polydimethylsiloxane-based deterministic lateral displacement devices

Polydimethylsiloxane (PDMS) is a popular material to rapidly manufacture microfluidic deterministic lateral displacement (DLD) devices for particle separation. However, manufacturing and operation challenges are encountered with decreasing device dimensions required to separate submicron particles. The smaller dimensions, notably, cause high hydraulic resistance, resulting in significant pressure even at relatively low throughputs. This high pressure can lead to PDMS deformation, which, in turn, influences the device performance. These effects may often be overlooked in the design and operation of devices but provide a systematic source of error and inaccuracies. This study focuses in detail on these effects and investigates pillar deformation in detail. Subsequently, we discuss a potential solution to this deformation using thermal annealing to stiffen the PDMS. We evaluate the influence of stiffness on the separation performance at elevated sample flow rates with submicron particles (0.45 and 0.97 µm diameter). An excellent separation performance at high throughput is successfully maintained in stiffer PDMS-based DLD devices, while the conventional devices showed decreased separation performance. However, the increased propensity for delamination constrains the maximal applicable throughput in stiffer devices. PDMS deformation measurements and numerical simulations are combined to derive an iterative model for calculating pressure distribution and PDMS deformation. Finally, the observed separation characteristics and encountered throughput constraints are explained with the iterative model. The results in this study underline the importance of considering pressure-induced effects for PDMS-based DLD devices, provide a potential mitigation of this effect, and introduce an approach for estimating pressure-induced deformation.

A layout-dependent formula for the critical separation size of parallelogram-type deterministic lateral displacement arrays

The accurate and general formulation of the critical separation size is crucial for the effective design and application of passive microfluidic devices. However, the current formulas for the deterministic lateral displacement (DLD) technique are inadequate in accounting for its structural complexity. To address this limitation, we conducted mesoscopic hydrodynamics simulations to assess the separation performance of various parallelogram-type circular post arrays. Based on the simulation results, we developed a new layout-dependent formula that takes into account key geometric parameters, such as the lateral gap size, row shift fraction, and aspect ratio of downstream and lateral post-post distances, to characterize the lateral gap dimension, periodicity, and asymmetry of DLD arrays, respectively. This formula demonstrated high accuracy over a wide design space, precisely predicting the critical separation sizes of many asymmetric DLD devices in experiments. Furthermore, it is worth noting that when the downstream gap size expands, the veering flow strengthens, which, in turn, results in an increase in the critical separation size. These findings shed light on the unique separation mechanism induced by array asymmetry and present a powerful design tool for maximizing the potential of asymmetric DLD devices.

Blood Cell Separation Using Polypropylene-Based Microfluidic Devices Based on Deterministic Lateral Displacement.

Mammalian blood cell separation methods contribute to improving the diagnosis and treatment of animal and human diseases. Microfluidic deterministic lateral displacement (DLD) devices can sort cells based on their particle diameter. We developed microfluidic DLD devices with poly(propylene)-based resin and used them to separate bovine and human red blood cells (RBCs) and white blood cells (WBCs) without electric devices. To determine the critical cut-off diameter (Dc) of these devices, we used immunobeads with a diameter of 1-20 μm. The Dc values of the microfluidic DLD devices for the immunobeads in the experiments were similar to the calculated Dc values (8-10 μm). Results from bovine blood cell separation experiments suggest that lymphocytes and neutrophils can be separated from diluted, whole blood. Human RBCs were occasionally observed in the left outlet where larger particles with diameters closer to the Dc value were collected. Based on the Dc values, human neutrophils were sorted to the left outlet, whereas lymphocytes were observed in both outlets. Although microfluidic channel optimization is required for the concentration of sorted cells, the microfluidic DLD device prepared with a poly(propylene)-based resin has the potential for clinical use.

Increasing flow rates in polydimethylsiloxane-based deterministic lateral displacement devices for sub-micrometer particle separation

In this study, we show the design and manufacturing of microfluidic deterministic lateral displacement (DLD) devices for sub-micrometer particle separation. For that purpose, devices with pillar gaps of 4 µm and a periodicity of 50 were designed. After photolithographic manufacturing of SU-8 masters with different heights (15 and 30 µm) and vertical sidewalls for soft-lithographic replication with polydimethylsiloxane (PDMS) the influence of flow rate on the separation efficiency of 0.45 and 0.97 µm particles was investigated. The 15 µm devices were operated at 0.125 and 0.5 µl/min sample flow rate and the 30 µm devices at 0.5 and 2.0 µl/min, respectively. Excellent separation efficiencies were observed for both device heights at the lower sample flow rates, while separation efficiencies decreased at the respective higher sample flow rates. The decrease in separation efficiency was attributed to deformation of the soft PDMS pillars, which causes an increase in pillar gaps at the higher sample flow rates as shown by microscopy imaging. The advantage of the 30 µm devices over the 15 µm devices is clearly shown by the separation of 0.45 and 0.97 µm particles at 0.5 µl/min. Due to reduced hydrodynamic resistance in the 30 µm devices and thus less pillar deformation, the displacement efficiency of 0.97 µm particles was above 99% compared to 46–57% for the 15 µm devices. Our 30 µm devices demonstrated excellent separation at a tenfold higher sample flow rate with 0.5 µl/min compared to comparable PDMS-based devices operating in the same size regime.

Effect of process parameters on separation efficiency in a deterministic lateral displacement device

Deterministic lateral displacement (DLD) is a hydrodynamic method known for its high-resolution sorting of particles. It achieves this through a periodic array of obstacles and laminar flow that passively directs particles along in two different directions depending on the particles’ diameter. Many prior publications have been dedicated to the structural and geometrical development of DLD arrays to improve separation performance; however, a successful separation requires much more than a well-designed array. This paper shows how separation performance is affected by process parameters. For this purpose, the design and fabrication of a DLD device are described. Then three experiments show how process parameters affect the performance of the device. The first experiment uses dye solutions to visualize the formation of a hydrodynamically focused sample stream. The second experiment shows that the particle separation performance (of 7- & 15-µm particles) is affected by the way output fluids are collected. Finally, the third experiment looks at the particle separation efficiency as the input flow rates and the ratio of buffer to sample are changed. The results show that the proper range for buffer and sample flow rate in this device is 1–10 and 0.1–1 (µl/min), respectively. The buffer to sample flow rate ratio of 10 gives the highest separation efficiency, but at a lower sample throughput. The optimized values are specific for our device but demonstrate processes that we believe are universal for DLD separations.

Metal Assisted Chemical Etch of Polycrystalline Silicon

Abstract Metal-assisted chemical etching (MacEtch) of silicon shows reliable vertical anisotropic wet etching only in single-crystal silicon, which limits its applications to a small number of devices. This work extends the capabilities of MacEtch to polysilicon which has potential to enable high-volume and cost-sensitive applications such as optical metasurfaces, anodes for high capacity and flexible batteries, electrostatic supercapacitors, sensors, nanofluidic deterministic lateral displacement devices, etc. This work presents a MacEtch of polysilicon that produces nanostructure arrays with sub-50 nm resolution and anisotropic profile. The three demonstrated structures are pillars of 5:1 aspect ratio and 50 nm spacing for comparison to single crystal silicon MacEtch literature, pillars of 30 nm spacing, and a diamond pillar array with sharp corners to establish resolution limits of polysilicon MacEtch.

Lubrication Force Saturation Matters for the Critical Separation Size of the Non-Colloidal Spherical Particle in the Deterministic Lateral Displacement Device

Deterministic lateral displacement (DLD) is a popular technique for separating micro-scale and nano-scale particles continuously. In this paper, an efficient three-dimensional fictitious domain method is developed for the direct numerical simulation of the motion of a non-colloidal spherical particle in the DLD device (i.e., cylinder array), based on substantial modification of our previous FD method. A combination of the fast Fourier transformation (FFT) and a tri-diagonal solver is developed to efficiently solve the pressure Poisson equation for a DLD unit with a shifted periodic boundary condition in the streamwise direction. The lubrication force correction is adopted in the fictitious domain method to correct the unresolved hydrodynamic force when the particle is close to the cylinder with the gap distance below one mesh, and the lubrication force is assumed to saturate at a smaller critical gap distance as a result of the surface roughness effect. The proposed method is then employed to investigate the effect of the critical gap distance of the lubrication force saturation on the motion mode (i.e., separation size) of the particle in the DLD device. Our results indicate that the lubrication force saturation is important to the particle critical separation size, and a smaller saturation distance generally makes the particle more prone to the zigzag mode.

Numerical simulation of critical particle size in asymmetrical deterministic lateral displacement

Microfluidics devices are widely used for particle separation. Deterministic Lateral Displacement (DLD) is a passive method for particle separation. DLD devices mainly separate particles based on their sizes. There are two main modes of movement in DLD arrays; the small particles move in a zigzag path, and the larger particles separate in the displacement mode. It is therefore important to estimate the critical particle size for the transition of modes before the fabrication of DLD devices. Asymmetry in the design of the arrays can affect the fluid behavior and the critical particle size. In this study, we investigate the effects of the asymmetry caused by changing the downstream gap size to the lateral gap size ratio on the fluid behavior and particle trajectories in DLD devices. We used two dimensional (2D) Finite Element Method (FEM) to study the variations in the flow lane's widths and combined the fluid analysis with structural mechanics to model the contact between the particles and the posts in DLD arrays. We simulated the spherical particles' trajectories with diameters ranging from 1.4 to 19.2 μm in circular post DLD arrays with a lateral gap size of 20μm. In contrast to the previous works, in these simulations, the effect of particle movement on the fluid flow profiles was considered. We evaluated the particle movement mode in seven different values of the downstream gap size to the lateral gap size ratio (ranging from 0.5 to 2) and eight different row shift fraction (ranging from 0.025 to 0.3). Our simulations showed that increasing the value of the downstream gap while the lateral gap is fixed increases the veering flow rate and width. By finding the particle with the largest diameter in the zigzag mode and the particle with the smallest diameter in the displacement mode, we estimated the critical particle diameter for each value of shift fraction in different values of the downstream gap to the lateral gap size ratio. Using these data, a curve was fitted for predicting the critical particle diameter in each ratio. Finally, a more general form of the formula for the critical particle diameter was proposed, which considers an extra parameter compared to the previous ones. The results of this study can lead to a better understanding of DLD devices' functions and, thus, save time and costs for better designs and experiments.

Combining Electrostatic, Hindrance and Diffusive Effects for Predicting Particle Transport and Separation Efficiency in Deterministic Lateral Displacement Microfluidic Devices.

Microfluidic separators based on Deterministic Lateral Displacement (DLD) constitute a promising technique for the label-free detection and separation of mesoscopic objects of biological interest, ranging from cells to exosomes. Owing to the simultaneous presence of different forces contributing to particle motion, a feasible theoretical approach for interpreting and anticipating the performance of DLD devices is yet to be developed. By combining the results of a recent study on electrostatic effects in DLD devices with an advection–diffusion model previously developed by our group, we here propose a fully predictive approach (i.e., ideally devoid of adjustable parameters) that includes the main physically relevant effects governing particle transport on the one hand, and that is amenable to numerical treatment at affordable computational expenses on the other. The approach proposed, based on ensemble statistics of stochastic particle trajectories, is validated by comparing/contrasting model predictions to available experimental data encompassing different particle dimensions. The comparison suggests that at low/moderate values of the flowrate the approach can yield an accurate prediction of the separation performance, thus making it a promising tool for designing device geometries and operating conditions in nanoscale applications of the DLD technique.

Effect of angle-of-attacks on deterministic lateral displacement (DLD) with symmetric airfoil pillars.

Deterministic lateral displacement (DLD) is a microfluidic technique for size fractionation of particles/cells in continuous flow with a great potential for biological and clinical applications. Growing interest of DLD devices in enabling high-throughput operation for practical applications, such as circulating tumor cell (CTC) separation, necessitates employing higher flow rates, leading to operation at moderate to high Reynolds number (Re) regimes. Recently, it has been shown that symmetric airfoil shaped pillars with neutral angle-of-attack (AoA) can be used for high-throughput design of DLD devices due to their mitigation of vortex effects and preservation of flow symmetry under high Re conditions. While high-Re operation with symmetric airfoil shaped pillars has been established, the effect of AoAs on the DLD performance has not been investigated. In this paper, we have characterized the airfoil DLD device with various AoAs. The transport behavior of microparticles has been observed and analyzed with various AoAs in realistic high-Re. Furthermore, we have modeled the flow fields and anisotropy in a representative airfoil pillar array, for both positive and negative AoA configurations. Unlike the conventional DLD device, lateral displacement has been suppressed with +5° and + 15° AoA configurations regardless of particle sizes. On the other hand, stronger lateral displacement has been seen with -5° and - 15° AoAs. This can be attributed to growing flow anisotropy as Re climbs, and significant expansion or compression of streamlines between airfoils with AoAs. The findings in this study can be utilized for the design and optimization of airfoil DLD microfluidic devices with various AoAs.

Electrokinetic biased deterministic lateral displacement: scaling analysis and simulations

Deterministic Lateral Displacement (DLD) is a microfluidic technique where arrays of micropillars within a microchannel deflect particles leading to size-based segregation. We recently demonstrated that applying AC electric fields orthogonal to the fluid flow increases the separation capabilities of these devices with a deflection angle that depends on the electric field magnitude and frequency. Particle deviation occurs in two distinct regimes depending on frequency. At high frequencies particles deviate due to negative dielectrophoresis (DEP). At low frequencies (below 1 kHz) particles oscillate perpendicular to the flow direction due to electrophoresis and are also deflected within the device. Significantly, the threshold electric field magnitude for the low frequency deviation is much lower than for deflection at high frequencies by DEP. In order to characterize the enhanced separation at low frequencies, the induced deviation was compared between the two frequency ranges. For high frequencies, we develop both theoretically and experimentally scaling laws for the dependence of particle deviation on several parameters, namely the amplitude of the applied voltage, particle size and liquid velocity where DEP forces compete with viscous drag. A novel theoretical framework is presented that enables simulation of particle trajectories subjected to DEP forces in DLD devices. Deviation angles predicted by simulations are in very good agreement with experimental data. At low frequencies (below 1 kHz), particles follow the same scaling law, but with much lower voltages. This indicates that electrokinetic phenomena other than DEP play an important role in driving particle behaviour. Experiments show that at low frequencies, particle motion is affected by quadrupolar electrohydrodynamic flows around the insulating pillars of the DLD array. We quantify the difference between the two frequency regimes and show that an electrokinetic model based only on DEP forces is limited to frequencies of 1 kHz and above.

The fluidic resistance of an array of obstacles and a method for improving boundaries in deterministic lateral displacement arrays

Deterministic lateral displacement (DLD) is a microfluidic method of separating particles by size. DLD relies on precise flow patterns to deliver high-resolution particle separation. These patterns determine which particles are displaced laterally, and which follow the flow direction. Prior research has demonstrated that the lateral array boundaries can be designed to improve the uniformity of the critical size and hence separation performance. A DLD device with an invariant critical size throughout is yet unknown. In this work, we propose a 3D design approach. We first represent the flow through the DLD as a 2D lattice of resistors. This is used to determine the relative flow resistances at the boundaries that will deliver the correct flux patterns. We then use the lattice Boltzmann method to simulate fluid flow in a 3D unit cell of the DLD and measure the fluidic resistance for a range or typical dimensions. The results of this work are used to create a new equation for fluidic resistance as a function of post size, post height, and post spacing. We use this equation to determine array geometries that should have the appropriate resistances. We then design and simulate (in COMSOL) complete devices and measure fluid fluxes and first flow-lane widths along the boundaries. We find that the first flow-lane widths are much more uniform than in any devices described previously. This work provides the best method for designing periodic boundaries, and enables narrower, shorter, and higher throughput DLD devices.

Accelerated Particle Separation in a DLD Device at Re > 1 Investigated by Means of µPIV.

A pressure resistant and optically accessible deterministic lateral displacement (DLD) device was designed and microfabricated from silicon and glass for high-throughput fractionation of particles between 3.0 and 7.0 µm comprising array segments of varying tilt angles with a post size of 5 µm. The design was supported by computational fluid dynamic (CFD) simulations using OpenFOAM software. Simulations indicated a change in the critical particle diameter for fractionation at higher Reynolds numbers. This was experimentally confirmed by microparticle image velocimetry (µPIV) in the DLD device with tracer particles of 0.86 µm. At Reynolds numbers above 8 an asymmetric flow field pattern between posts could be observed. Furthermore, the new DLD device allowed successful fractionation of 2 µm and 5 µm fluorescent polystyrene particles at Re = 0.5–25.